[28/06/2001] An article by Alison George, based on a talk I gave,
in the
Grauniad,
or I have archived it here. Its not actually terribly clear: some time I must rant about journalists...

To clarify a little: I am interested in "Was an imminent Ice Age predicted in the '70's
by scientists, in scientific journals?".
That means articles in scientific journals and reputable
books. I am not particularly interested in what appeared in the popular press
or on TV and do not intend to discuss it here
(but see
context), since I do not regard these
as reliable sources for scientific information.

Note that many of the oh-there-was-an-ice-age-predicted type articles tend to
focus on non-science articles for their sources: newsweek, for example. This is
cheating on their part. Newsweek isn't science, of course. If newsweek was quoting
peer-reviewed journals, then they should go back to those.

We also need to know what we mean by "imminent". Since the question arises in the context of
the greenhouse gas/climate change debate, "imminent" is a timescale comparable to greenhouse-type
timescales: ie, the next century or so. See below for my take on long-term predictions.

If you think you have a new reference that may be interesting, please send it to me.
I don't guarantee to check it out immeadiately: you will need to have patience.
However, I will list all outstanding references below:

Just in: these 2 both mention a 1972 letter, amongst other things. Interesting! I haven't
read them properly yet.

The purpose of this page is to provide a counter to the
mythology that "journals were stuffed full of
articles predicting an imminent ice age in the '70's".
An article by the
John Birch
Society seems to be an example of the kind of thing [oops, they've changed the page! I should have
copied the old one... happily, JS points me to:
the web.archive.org's archive of it]
(see also "The New Australian", or
http://www.ff.org/library/whatsnext.html [local cache]),
and it even appears in milder form in the 1999 Reith lectures.
The relevance of
this claim is that "greenhouse sceptics" are fond of claiming that
"all scientists" were predicting cooling a decade ago and now they've
switched to warming. However, closer probing reveals few of these articles.

The argument has two very seperate strands: the "orbital-forcing" strand,
wherein the cooling was to occur as a result of variations in the Earths
orbit around the sun, and the "aerosols" strand, which supposed cooling in
response to a massive increase in the aerosol loading of the atmosphere.
In fact there is a variant of the first idea, rapid climate change during
interglacials, see
Flohn, 1979.

I have been reminded of the following posts:
Cooling vs. Warming by Robert Parson in 1993 and
Re: control the climate by Michael Tobis in 1995.
My summary of the first of these posts is (shamelessly ripped from the post
itself): everyone agreed that CO2
emissions could produce warming and that particle emissions could
produce cooling, but that lack of information precluded any definite
conclusions about which was more important.
The second is harder to summarise (why not just read it?) but suggests that
predictions of cooling were
made by observational
paleoclimatologists rather than physical climatologists
and were based on dubious and non-physical
arguments.
Franz Gerl reminds us that a report to the Carter administration
in 1980
predicted warming.

The following paragraph is cut from the Cato Insitute. Its by Richard Lindzen, generally considered a skeptic.
I wouldn't agree with all of (especially the tone ;-) but its description of the cooling scare as
"minor" and "the scientific community never took the issue to heart, governments ignored it" is good.

Many studies from the nineteenth century on suggested that industrial
and other contributions to increasing carbon dioxide might lead to
global warming. Problems with such predictions were also long noted,
and the general failure of such predictions to explain the observed
record caused the field of climatology as a whole to regard the
suggested mechanisms as suspect. Indeed, the global cooling trend of
the
1950s and 1960s led to a minor global cooling hysteria in the 1970s.
All that was more or less normal scientific debate, although the
cooling hysteria had certain striking analogues to the present warming
hysteria including books such as The Genesis Strategy by
Stephen Schneider and Climate Change and World Affairs by Crispin
Tickell--both authors are prominent in support of the present
concerns as well--"explaining'' the problem and promoting international
regulation. There was also a book by the prominent science
writer Lowell Ponte (The Cooling) that derided the skeptics and noted
the importance of acting in the absence of firm, scientific
foundation. There was even a report by the National Research Council of
the U.S. National Academy of Sciences reaching its usual
ambiguous conclusions. But the scientific community never took the
issue to heart, governments ignored it, and with rising global
temperatures in the late 1970s the issue more or less died. In the
meantime, model calculations--especially at the Geophysical Fluid
Dynamics Laboratory at Princeton--continued to predict substantial
warming due to increasing carbon dioxide. Those predictions
were considered interesting, but largely academic, exercises--even by
the scientists involved.

Here are two references dug out by the IceAgePredictors,
representing the two strands mentioned above.

Future climate. Having presented evidence that major changes in past
climate were associated with variations in the geometry of the earth's
orbit, we should be able to predict the trend of future climate. Such forecasts
must be qualified in two ways. First, they apply only to the natural component
of future climatic trends - and not to anthropogenic
effects such as those due to the burning of fossil fuels. Second, they
describe only the long-term trends, because they are linked to orbital
variations with periods of 20,000 years and longer. Climatic oscillations
at higher frequencies are not predicted.

One approach to forecasting the natural long-term climate trend is to
estimate the time constants of response necessary to explain the observed phase
relationships between orbital variation and climatic change, and then to use
those time constants in the exponential-response model. When such a model
is applied to Vernekar's (39) astronomical projections, the results
indicate that the long-term trend over the next 20,000 years is towards
extensive Northern Hemisphere glaciation and cooler climate (80).

The claims and counter-claims that were posted are
here.
The article investigates effects of large CO2 and aerosol
perturbations. Large enough aerosol increases lead to large temperature drops,
whereas even large CO2 increases "only" lead to changes of 2 oC.
There is some discussion of likely aerosol or CO2 increases.

While I'm here, note that "opponents" of Schneider generally mention "a paper
by Schneider" and rarely report that he was the second author. Presumably
this is because demonising Rasool wouldn't serve their purposes. Alternatively,
it may be because few people have actually read the paper, and rely on
secondary sources for information (including authorship) about it.

The article does not predict the future climate of the Earth. It does attempt
to predict the climate sensitivity to CO2 and aerosol forcings.
The predicted CO2 sensitivity would now be regarded as rather low
(and a footnote points out that at the same time other authors found
sensitivities three times as large). A second footnote points out that the
sort of model used (a 1-d radiative model) is only suitable for examining
the effects of small perturbations about current climate values
(a qualification that applies to many models nowadays, too), but
fails to note the inherent contradiction with the title of the paper.

The concluding section contains some guesses towards future aerosol levels.
Quoting: "Even if we assume that the rate of scavenging and of other
removal processes for atmospheric dust [generally
& confusingly used interchangably
with aerosol in the article (WMC)]
particles remains constant, it is still difficult to predict the rate at which
global background opacity of the atmosphere will increase with increasing
particulate injection by human activities. However, it is projected that man's
potential to pollute will increase 6 to 8-fold in the next 50 years. If
this increased rate of injection... should raise the present background opacity
by a factor of 4, our calculations suggest a decrease in global temperature
by as much as 3.5 oC. Such a large decrease in the average temperature of
Earth, sustained over a period of few years, is believed to be sufficient to
trigger an ice age. However, by that time, nuclear power may have largely
replaced fossil fuels as a means of energy production."

Other people have other takes on this paper:
John Daly is the most obvious.
It is worth pointing out that Dalys page contains several mistakes - for example,
he claims that "This means that Schneider's conclusions would be just as valid today".
Daly is perfectly well aware that the Schneider paper uses incorrect (a fact of 3 too low)
values for CO2 sensitivity, rendering the conclusions invalid in the
light of todays science - he just doesn't choose to put that fact onto the page.

GoogleWatch: a sample of some usenet posts about this paper: must add more sometime:

people critise R+S for being hopelessly, laughably wrong. Clearly
their estimates of the aerosol increase were wrong, but I know of no
source showing that their scientific analysis of the response of
climate to increased aerosol was wrong.

I've raised this point in sci.environment on occaision. The best response
I've had is a ref to a comment by Gast in a succeeding issue of Science.
But his point doesn't address my question above.
Gast notes that dT is linear in aerosol, as far as he
can see, and that R+S's figures, being logarithmic, are misleading.
But this has no relevance to the numbers R+S produce. Gast also
(probably correctly) points out that anthro aerosol is only 1/5 of the
total, and hence an 8x increase in anthro aerosol wouldn't increase the
total by 8x but 2-4x, thus reducing R+S's numbers. But again this is
irrelevant to the science that R+S is presenting. So the question
remains: when R+S say that and increase in (total) aerosol by a
factor of 8x would leading to cooling of ?3.5K? and this could lead to
a new ice age, is that wrong or not? Was is rebutted soon after,
more recently, or not at all?

[Don Libby attempted to use results from the IPCC SAR,
see
here which were very
tentative,
but might be read to indicate that R+S weren't too far wrong.]

ps: to show that R+S weren't as far out on a limb as often asserted,
note that the letter following Gast broadly supports R+S's numbers.